FI98051C - Procedure for removing tin compounds from exhaust gases - Google Patents

Description

98051

Method for Separating Tin Compounds from Exhaust Gases This patent application is a continuation of earlier U.S. Patent -5 Application Serial No. 406,482, filed September 13, 1989.

This invention relates to the removal of metal species from gases. Even more particularly, the present invention relates to the removal of metal halide or organometallic halide species from exhaust gases released during manufacturing processes, and is particularly useful for removing tin-containing species from exhaust gases.

Numerous industrial processes release metal-15 gases into the atmosphere; limits have been set to protect the environment and are constantly being reviewed for the amount of metals that can be released in this way. This may require changes to or even rejection of inefficiently or poorly controlled processes; alternatively, additional processing steps may be necessary to remove the metal species to allow the process to continue. Such well-known processes use various methods, such as scrubbing the exhaust gases with water, filters with absorbent solids, e.g., coal, burning the exhaust gases to ash, and passing the gases through dust filters or electrostatic precipitators.

U.S. Patent Nos. 4,144,262 and 4,130,673 to Larkin and U.S. Patent No. 4,530,857 to Lindner disclose treating the newly formed 30 and still hot glass bodies with monobutyl tin trichloride (MBTC) vapors to form a protective tin oxide layer on the surfaces of the bodies and a concomitant MBTC. removal from the exhaust gases of that process. They recommend electrostatic precipitators or other equipment.

To solve the problem of waste stream removal, there is another means known per se for contacting the exhaust gases with an aqueous solution of a base such as sodium hydroxide. However, it has been found that known exhaust gas treatment methods suffer from numerous drawbacks; most methods do not achieve the required low concentrations of metals to allow free removal of purified exhaust gases. This is the case if, for example, an electrostatic precipitator or seal is used.

Washing with an alkaline solution generates an aqueous metal oxide, the oxide containing sludge, which again has to be treated by filtration or centrifugation, thus creating a new wastewater disposal problem. This method is also expensive and requires uneconomical labor.

The essential features of the present invention are set out in the appended claims.

The method of the present invention comprises: (a) contacting metal species-containing gases with an acidic aqueous medium having a pH of less than about 6 and preferably less than about 2 to absorb substantial amounts of metal species from the gas to a level that allows the gas to enter the atmosphere; already 25 contains a minimum amount of metal to be absorbed, (b) optionally recycling the acidic aqueous medium to increase the metal content in the solution, 30 (c) optionally using the metal-containing solution to recover the accumulated metal as a metal, metal oxide or organometallic compound, and (d) all of the solution; re-use in a process that generates metal-containing gases to at least partially replace the metal compounds used.

3 98051

The figure is a schematic partial view of the apparatus used in a preferred embodiment of the present invention.

The present invention comprises a method for removing metal- and especially tin-containing species from the gases leaving the exhaust gases from a plant used for coating glass objects with a layer of tin oxide, the material thus formed, and the apparatus with which the method is carried out.

The method of the present invention makes it possible to relatively simply purify the exhaust gases from a glass tin compound coating operation. It also avoids the formation of solid waste and prevents the formation of tin-containing wastewater 15, e.g. in a glass factory. The present method makes it possible to purify the exhaust gases to a concentration of less than 5 mg of tin metal per standard cubic meter of gas, as is required, for example, in the Federal Republic of Germany.

20 The aqueous medium is easiest to purify in the manufacturing process of the tin compound. Once this recycling is completed, no further treatment of the aqueous medium is required from the glass manufacturer, and the process does not produce waste materials. Such purification is economically possible due to the high metal content achievable, which makes it possible to store and transport the washing solution resulting from the contact of the acidic aqueous medium with the gas. It is also possible to completely or partially purify the wash solution back to a process that generates vapors containing metal-30 to replace some of the pure metal compound required. Since total purification in the latter process results in most cases in an increasing high acid content in the washing solution, it may be economically advantageous to purify at least a portion of the washing solution in the metal-35 compound manufacturing process.

A suitable medium for initiation is one that is predominantly water containing an oxidant to prevent or reduce the precipitation of 4,98051 solids. Due to recycling, the concentration of metal species can be easily increased to the desired level.

The present process is particularly suitable for use in a process in which glass or similar substrates are coated with tin oxide and in which the residue is removed from the exhaust gases coming from the coating plant. The recommended tin content of the contact solutions is about 5% by weight of tin metal while maintaining the pH at about 6, preferably about 2.5, and most preferably less than about 2. Tin metal concentrations of preferably about 10% by weight and more preferably about 20% by weight.

The exhaust gas can be contacted with the liquid medium 15 in a high-performance scrubber. However, according to a preferred embodiment of the present invention, the gas is contacted with the liquid medium in a low power scrubber or spray tower under conditions that prevent the formation of mist.

20

It is expedient to always keep the gases at a temperature above the evaporation point of the tin species. This can be done by adding additional heat to prevent the formation of local conditions for gases with tin-containing species. According to one embodiment, steam is added to the exhaust gases to prevent local cooling of the scrubbing solution in the scrubber. It is recommended that the vapors be kept above the evaporation point of the tin species. In another preferred embodiment, the wash solution is heated by circulating it through a heat exchanger. The present method is particularly suitable for use with tin tetrachloride, alkyltin halide or MBTC.

It is known that already dilute aqueous solutions of MBTC have a strong tendency to foam; this interferes with the handling of gases in scrubbing systems. Surprisingly, however, it has now been found that the present method can be used with high concentrations of tin in a washing solution without generating significant amounts of foam.

According to the present invention, the second device 5 can be used with a more dilute solution of a tin compound in water in the second step to further reduce the metal content of the gas if either the economics of the process or environmental considerations would require further treatment. In addition, the invention provides an apparatus and by-product solution enriched in metal-10 species and other degradation products.

It will be appreciated that the concentrated solutions may be used in the manufacturing process from which the exhaust gases have been originally removed or in the manufacturing process of the tin compound. However, it is also possible to transport the concentrated solution to a plant located elsewhere to recover the metal content. Finally, due to the relatively low tin content of the gases to be removed, the method of the present invention is useful in geographical areas where stricter regulations apply to emissions harmful to the atmosphere.

The invention also encompasses processes that generally use metal species in manufacturing or processing and the process used to remove metal species from all exhaust gases.

The gases from the removal or plant processes containing the metal species are contacted with the aqueous medium under certain conditions of time, temperature, mixing and medium to allow a substantial amount of the metal species to be absorbed into the aqueous fraction while keeping the resulting composition substantially free of precipitation; the resulting solution can therefore be used until a significant concentration of metal species is reached, which allows the economic treatment of a solution of metals, especially tin and tin-containing species. At the same time, the process makes it possible to purify the effluents to a metal content of less than 5 mg / standard m3. Such results cannot be obtained by methods known per se 6 98051; current methods using condensers, filters or electrostatic precipitators do not result in exhaust gases containing sufficiently low concentrations of metal species. Methods using alkaline aqueous media can achieve this goal, but they are quite laborious and laborious.

For example, in known processes, when contacting the exhaust gases with an alkaline solution, it is necessary to remove 10 continuously formed precipitates, which makes the operation difficult because the precipitates of tin compounds are known to be difficult to filter. Filtration and centrifugation are foreign to the industry, and the processes produce effluent of a quality that is not permitted to be discharged into a waste water or other installation without further treatment of this effluent; contacting the exhaust gases exclusively with water, which is constantly being regenerated, produces large quantities of waste water which also needs to be further treated.

20 Surprisingly, and contrary to the expectations based on the calculations of the vapor pressures of the tin compounds in question, it has been found that a solution containing significant amounts of tin-containing species and optionally hydrochloric acid or other acids can be used as a contact medium for exhaust gas cleaning. Utilizing the apparatus of the present invention, it has unexpectedly been found possible to use contact solutions containing more than 5, preferably more than 10, and most preferably more than 20% by weight of tin, calculated as tin metal, keeping the pH of the process medium below about 6.

Contacting between the liquid and gas fractions is best accomplished by a number of methods, including both static and active mixing, but is best accomplished by active mixing of the two fractions. The gas can simply be bubbled through the aqueous medium stored in the tank, or the aqueous medium can be mixed as the steam enters the air space above the liquid. In one embodiment, the gas is contacted with a liquid medium in a high power scrubber.

In a preferred procedure, the liquid medium 5 is contacted with the gas in a low-power scrubber or spray tower under conditions which promote the evaporation of the gas containing tin-containing species. According to the method of the present invention, it is possible to avoid the use of a high-power scrubber and to use a cheaper low-power hop-10 Sur if the steam is prevented from becoming supersaturated by tin-containing species. Unexpectedly, it has been found that metal-containing species can be removed from gases relatively easily and below concentrations predictable from the calculated vapor pressures of the compounds present in their wash solution if the gases are kept above the saturation points of the species involved.

If the gases are allowed to cool to their saturation point, it is quite difficult to separate the fine mist or sol of the resulting liquid containing metal and especially tin compounds 20 from the gas. In the latter case, more equipment and more energy-intensive methods must be used to separate the mist or sol from the gas.

The present invention comprises a method of using an acidic aqueous solution to obtain a relatively high content of metal compounds in a washing solution. The degree of acidity of the washing solution, which is necessary to prevent the formation of a precipitate and foaming, can be achieved by starting with process water acidified with, for example, hydrochloric acid or another suitable inorganic acid.

It is in the spirit and object of the present invention to start the water treatment step with water which already contains an intentionally added amount of metal or organometallic halide, such as MBTC, which gives the required level of acidity. In the process, it is hardly necessary to add more acid or tin compound later if the exhaust gases contain oxygen, such as hydrogen halide. In that case, the process automatically maintains the required level of acidity.

The process of this invention can be performed over a wide thermal range; it is usually advisable to use ambient temperature for simplicity and economy. If low power scrubbers are used, additional heat addition means may be advantageous to prevent local supersaturation conditions for the gas with a liquid containing metal species such as tin halides and organometallic halides, silanes and the like. In addition, steam can be added to the exhaust gases to prevent local cooling of the scrubbing solution due to evaporation due to the low relative humidity of the environment.

15

In the event that the exhaust gases are very hot, as they may be in some glass coating processes, it may be necessary to cool the circulating fluid or exhaust gases. Cooling of gases, liquids or equipment can be performed by methods well known in the art, which methods do not in themselves form any part of this invention.

The required contact time between the exhaust gases and the scrubbing liquid depends on the detectable amount of the metal compound in the exhaust gas which is removed to the atmosphere following the process treatment method of the present invention. The process is continued long enough until the effluent criteria are met. For this purpose, it may be advantageous to use one relatively large washing tower or similar device, or to use a number of smaller devices in series. The latter option also allows the metal content of the compounds removed from the equipment to be further increased to recover them; the scrubbing solution circulates 35 in the apparatus until the concentration of the metal part of the solution exceeds the limit, which allows efficient cleaning of the exhaust gases. This limit may vary as a function of temperature or equipment design parameters and must be determined in advance depending on the conditions.

By purifying the exhaust gases in a process in which the glass is coated with tin oxide using MBTC as the parent nuclide, the highest concentrations in the washing solution of more than 5 and preferably more than 10% by weight, calculated as tin metal, can be achieved. In the case where there is more than one washing device in the series, and by using the washing liquid of one washing device to supply the former, the tin content of the first device can reach 20% by weight or more. The performance of the device can be easily controlled by measuring some physical parameter, such as density, to adjust the concentration of the washing solution. In the event that more than one device is used in a series, a predetermined level can be maintained by replacing part of the liquid with water or washing liquid from the downstream washing device.

In a preferred embodiment of the invention, the apparatus 20 for removing metal species from the gases flowing from the process is connected to receive the exhaust gases from the apparatus for coating the glass bodies with tin oxide. Numerous tin compounds are known to be useful for this purpose; such compounds include, but are not limited to, MBTC, tin tetrachloride, dimethyltin dichloride, dibutyltin diacetate, monomethyltin sodium trichloride, and the like. Particularly preferred compounds are tin tetrachloride and alkyltin trichlorides such as MBTC. Descriptions of such tin compounds can be found e.g.

U.S. Patent Nos. 4,530,857, 4,144,362 and 4,130,673. The process of this invention is useful for removing tin compounds and their metal-containing reaction or decomposition products from the exhaust gases of such processes. At the same time, the process of the invention removes substantially all hydrochloric acid or other acids that may have formed during the coating process from the exhaust gases.

10 98051

Therefore, the present invention encompasses a process for removing metal species and reaction products from exhaust gases resulting from coating with tin compounds, the process comprising the steps of: (a) coating a glass substrate at a temperature between about 350 and about 650 ° C with steam or fines of at least one tin compound; capable of forming a tin oxide layer on the surface of the glass substrate under these conditions; (b) contacting the exhaust gases of this process, which gases may contain reaction products or unreacted portions of tin compounds, with an aqueous acidic scrubbing solution 15 to reduce the tin content in the exhaust gases; (c) recycling the scrubbing solution until it contains more than about 5% and preferably more than about 10% tin metal. in the form of the parent tin compounds or as reaction or decomposition products thereof; and (d) using a washing solution to recover tin compounds or tin metal.

In various embodiments, the glass substrate is a bottle or other glass container, flat glass, tubular glass products, and the like. The tin compound may be tin tetrachloride, MTBC or other glass treatment compound, and may be used alone or in compositions containing other organic or inorganic aliquots.

The following examples illustrate and illustrate the effect of metal content on the scrubbing solution, and the temperature and relative humidity of the gas to be scrubbed, as well as the residual metal content of the gas species leaving the scrubber.

98051

Example 1 In this example, 7 m3 of 20 ° C dry air was humidified to a predetermined relative humidity to 20 ° C. 0.7 m3 of this air was then heated and loaded with 2.66 g of 5 MBCT, passed through a glass tube heated to 550 ° C and then combined with the remaining 6.3 m3 of air. Using this approach, an average of 30% of the MBTC used remains in the glass tube in the form of tin oxide, and the remaining gas mimics closely the method of pin-10 weaving glass vessels with a layer of tin oxide by treating it with MBTC steam.

The gas was maintained at the existing temperature and first passed through a first glass column filled with glass rings, 80 mm in diameter and 300 mm in length; a 3% aqueous hydrochloric acid solution was circulated through the column. After leaving the first column, the gas passed through a second column 80 mm in diameter and 300 mm in length and also filled with glass rings. Tap water was circulated through the second column, and the solution from this column was used to replenish the liquid from the first column in order to maintain the desired MBTC concentration in this first column. The tin content at the outlet of the second column was measured. The tin metal concentration in milligrams per 25 standard cubic meters is given in the tables below.

Contrary to expectations, it was found that the washing solution could tolerate tin contents of at least 20% by weight and that it has a beneficial effect on the efficiency of the washing process. The results also show an increase in the absorption of the tin compound together with a higher relative humidity and a higher gas inlet temperature. 1

Not to be bound by the theory presented herein, one possible explanation is that the conditions of the examples presented herein, contrary to expectations, help to prevent fine misting of the products to be removed. Removal of such mists 12,98051 from gases has been found to be quite difficult by washing or other means known per se.

The finding that washing with a solution that already contains a substantial amount of product to be removed helps to solve a number of difficult gas purification problems and is an unexpected and important improvement that eliminates difficult methods such as washing with alkaline gas and centrifuging or filtering the resulting fines. -10 tion while lowering the filtrate through another wastewater treatment system. In addition, it is unnecessary to use high-power gas scrubbers or electrostatic precipitators, and the volume of the formed solution is significantly reduced, which leads to additional economics in the treatment of potentially harmful effluents from the process.

Tin content after gas scrubbing Milligrams of tin / cubic meter Table I

20 Inlet temperature Relative humidity% at 20 ° C 40 ° C 7 50 100 125

Washing solution Sn% Density 25 3 1.05 5 7 5 10 6 1.10 20 9 2 8 1.15 1.5 - 2 11 1.20 1.5 - 2 2 14 1.25 1.5 - 2 2 30 17 1.30 1.5 - 2 2.5 20 1.35 2 6 35 13 98051

Table II

Inlet temperature Relative humidity% at 20 ° C 50 ° C 7 50 100 125 5 Washing solution

Sn% Density 3 1.05 6 6 3.5 3.5 6 1.10 5 4 1.5 1.5 8 1.15 3.5 2.5 - 1.5 10 11 1.20 1.5 1.5 - 1.5 14 1.25 1.5 --22 17 1.30 1.5 - 2 2.5 20 1.35 2 .... g

15 Table III

Inlet temperature Relative humidity% at 20 ° C 60 ° C 7 50 100 125

Washing solution 20 Sn% Density 3 1.05 3.5 - - 3 6 1.10 10 4 --2 8 1.15 1.5 1.5 - 1.5 11 1.20 1.5 - 2 2.5 25 14 1.25 1.5 - 1.5 1.5 17 1.30 2 - 1.5 20 1.35 22--4

Example II

The following examples illustrate the effect of the MBTC content and one of its degradation products, hydrochloric acid, on the formation of foam in the wash solution.

Through a volume of 35 to 20 ml in a test tube 200 mm long and 24 mm in diameter, 70 l of nitrogen per hour were passed through a 3 mm internal polytetrafluoroethylene tube. The composition of the solution was given in the tables below. When the resulting foam had reached a constant height, 14,98051 it was measured; the height of the foam is given in the tables in mm.

The tables show that at relatively high MBTC concentrations, foaming was reduced to quite acceptable levels. In addition, there is a surprisingly beneficial effect of an increased concentration of the degradation product, hydrochloric acid. The amount of foaming also depended on the quality of the wash water. As can be seen from the results, relatively small amounts of MBTC 10 are sufficient to significantly generate foam, making the use of otherwise untreated water in the washer impossible.

Table IV

Foam formation in mm with different concentrations of hydrochloric acid and MBTC in tap water.

(German hardness 9 °) HCl content

Mol / l 0 0.025 0.05 0.1 0.15 0.2 0.25 0.337 0.5 g / 1 0 0.9 1.8 3.7 5.5 7.3 9.1 12.3 18 .3 20__ MBTC pit.

Mol / lg / i 0 0 10 - - - - - --25 0.018 5.1 - - - - - - - - 0.035 9.9> 140 - - - - - - - - 0.053 15, and 0.071 20.0> 140 - 75 - - 40 - - 30 0.089 25.1 30 0.133 37.5> 140 100 75 - 70 - 30 - 20 0,177 49,9> 140 - 100 - 40 0,266 63,8 30 - - - - - - 0,354 99,9 15 - - - - - - 20 35 15 98051

Table V

Foam formation in mm with different concentrations of hydrochloric acid and MBTC in demineralized water 5 Hydrochloric acid content

Mol / 1 0 0.025 0.05 0.1 0.15 0.2 0.25 0.337 0.5 g / 1 0 0.9 1.8 3.7 5.5 7.3 9.1 12.3 18 , 3 MBTC-10 pit.

Mol / 1 g / 10 0 10 - - - - - 0.018 5.1 40 40 40 40 30 30 25 25 25 0.035 9.9> 140 140 80 70 40 30 25 30 25 15 0.053 15, 0> 140 100 80 40 35 - - - 25 0,071 20,0 70 50 50 35 - - - - 20 0,089 25,1 35 - 30 - - - - - 20 0.133 37.5 20 - - - - - - - 20 20 The drawing diagram illustrates an apparatus with which the method of the present invention is performed. The exhaust pipe 102 may be connected to a plant for coating the glass or other material with a tin oxide layer or to another plant which generates exhaust gases containing metal species. The described apparatus is not intended to limit the scope of the invention to this particular embodiment; as a result of this description, other means for carrying out the present invention will become apparent to those skilled in the art.

Exhaust gases to be cleaned of tin or other metal species are forced from a production or coating plant not described at atmospheric or processing pressure through the process inlet line 102 and the process outlet line 103 as a result of reduced pressure in line 102 caused by a fan 104. The gas flow is measured by a flow meter 106 in the outlet line 107 of the fan 104.

The steam flow from the external source 108 is fed through a pipe 105 and a valve 109 to the circulation pipe 110 of the first scrubber 1698051 to keep the circulating liquid 124 above the dew point of the exhaust gases at all times. In this example, dual gas scrubbers 112 and 116 are used, although it will be apparent to those skilled in the art that, in accordance with the spirit and purpose of the present invention, either a single or multiple installation may be used. The arrangement described allows the tin content in the first scrubber to be maintained at about 15% by weight, calculated as tin metal. The concentration of solution 124 is kept substantially constant by a first specific gravity meter 114 which supplies additional dilution solution 118 to the first scrubber 112 from the second scrubber 116 through the tube 113 and the valve 111. If the surface of the liquid 124 in the scrubber 112 rises too high, the level control 120 opens the bottom valve 122 to allow some liquid to pass through the pipe 141 into the storage tank 142.

From the first scrubber 112, the gases pass through a guide tube 115 to a second scrubber 116 having a separate fluid circulation circuit 126 for circulating the medium 118 to make suitable contact with the effluent and treatment solution 118.

As the surface level of the liquid 118 decreases, the level control 128 opens the water inlet valve 130 to maintain the level of the functionally suitable liquid. Optionally, if the tin content of the second scrubber 116 becomes less than about 1% by weight, the second specific gravity regulator 132 may supply liquid 124 from the first scrubber 112 to the second scrubber 116 through the tube 117 and valve 133 30 to maintain required acidity and prevent foam and precipitation. However, it has surprisingly been found that when the substance removed is MBTC, this additional step is unnecessary. Therefore, in one embodiment of the invention, neither tube 117 nor another specific gravity regulator 132 is used.

35 At start-up, some hydrochloric acid is added to each liquid tank; then the acidity is retained by the hydrogen chloride in the exhaust gases.

17 98051

Pumps 134 and 136 circulate scrubbing fluids 124 and 118 in scrubbers 112 and 116 filled with a suitable packaging material, such as glass coils, porcelain or polymer needles, or the like. The pump 138 acts as a discharger for the storage tank 5 142 controlled by valves 152 and 153 through pipes 143 and 144 to a tanker or other transport vehicle or to a recycling and recovery facility not described, and does not in itself form part of the present invention.

In one assay of the utility of the present invention, exhaust air was taken into the unit as previously described from a glass coating apparatus installed after ten bottle blowing machines. The exhaust air was 90 m3 per minute and contained an average of 15,130 mg of tin, calculated as tin metal and about 140 mg of hydrochloric acid per standard cubic meter, calculated as HCL. The exhaust gas inlet temperature was between 50 and 70 ° C depending on the conditions of the glass manufacturing plant. Analysis of the gas leaving the exhaust pipe 107 showed that the tin content, calculated as tin metal, was always less than 5 mg per standard cubic meter of exhaust gas. The equipment produced 105 kg of solution per day, which contained about 16 kg of tin, calculated as tin metal. Modifications and improvements may occur to those skilled in the art encompassing the principles and guidelines of the preferred embodiments of the invention disclosed and described herein. Accordingly, the scope of the patent to be disclosed is not limited to the embodiments of the invention disclosed herein, but rather should be limited to the improvements on which the invention is based.

Claims (18)

1. For use in the manufacture of a medium, such as tetrachloride, alkyl tetrachloride or anhydrous compound for the treatment of a substance, which can be used as a medium in the form of a water absorber, for example, In the form of a dimer with a pH of about 6 or more, the color is shown above the image or the value of the absorber in the form of a mixture of about 5% by weight. 25 A process for treating exhaust gases comprising at least one tin compound which is tin tetrachloride, alkyltin halide or a mixture thereof, for removing said tin compound, characterized in that the exhaust gases are contacted with an aqueous, acidic, liquid, absorbent medium which does not not in the form of a mist, and having a pH of about 6 or less, thereby preventing the formation of a precipitate or foam, to absorb said at least 10 single tin compounds from the exhaust gases until the absorbent medium contains at least 5% by weight of tin. 2. A method according to claim 1, wherein the pH of the absorber is mediated by about 3. A method according to claim 1, characterized in that the pH of the absorbent medium is less than about 3. 15 3. A method according to claim 1, which can be adjusted to pH 30 for an absorbent medium of at least 2. The method of claim 1, wherein the pH of the absorbent medium is less than about 2. 4. A patent according to claim 1, which comprises the absorption of a redundant form which is suitable for use as an ink. 35 Method according to Claim 1, characterized in that the absorbing medium already contains at least one tin compound before it is brought into contact with the exhaust gas. 5. A patent according to claim 4, which can be used to reduce the absorption of the absorber according to claim 98051 and to circulate the absorber according to the invention. A method according to claim 4, characterized in that the presence of at least one tin compound in the absorbent medium is due to the recycling of the absorbent medium in the process. 6. A patent according to claim 4, which relates to an absorber according to claim 5, and which comprises the incorporation of an absorber according to the invention. A method according to claim 4, characterized in that the at least one tin compound present in the absorbent medium is incorporated therein before the absorbent medium is used. 7. A preferred embodiment according to claim 1, which comprises a crystal according to claim 10 having an absorbent content of less than 10% by weight. The method of claim 1, characterized in that the contacting is continued until the absorbent medium contains at least about 10% by weight of tin. 98051 8. A preferred embodiment according to claim 1, which comprises the use of an absorber with an absorbent content of about 20% by weight. The method of claim 1, characterized in that the contacting is continued until the absorbent medium contains at least about 20% by weight of tin. 9. An application for a patent according to the invention, which comprises a ring and is absorbed by the absorber, after which it is possible to carry out the invention. A method according to claim 1, characterized in that the exhaust gases are brought into contact with the absorbent medium without substantially impregnating the absorbent medium with said tin compound. 10. An application is made for a patent, which is intended to be used for the purpose of providing an absorbent medium. 25 The method of claim 1, further comprising recovering said at least one tin compound from an absorbent medium. 11. A preferred embodiment of claim 1, wherein the reducing agent is reduced to about 5 mg per standard cubic meter or less. 12. A compound according to claim 1, which comprises the use of monobutyl tetrachloride. A method according to claim 1, characterized in that the exhaust gases are purified to a tin content of about 5 mg per standard cubic meter or less. Process according to Claim 1, characterized in that the tin compound comprises monobutyltin trichloride. 20 13. A method according to claim 1, which comprises the treatment of monobutyltetrichlorides and the use of monobutyltetrichlorides in the form of absorbers. 98051 Process according to Claim 1, characterized in that the tin compound is monobutyltin trichloride and is recovered as monobutyltin trichloride from an absorbent medium. 25 14. A patent according to the invention, comprising the invention, is preferably absorbed after the application of the invention. 15. A preferred embodiment according to claim 1, which comprises an absorbent medium having the same properties as the water or an absorbent medium. A method according to claim 1, characterized in that the spent tin-containing absorbent medium is removed from the process and stored. 15 Patentkrav A method according to claim 1, characterized in that the absorbent medium used is removed and replaced with water or a more dilute absorbent medium. 16. A patent according to the invention, which comprises a ring according to claim 10, is provided with an absorbent medium or a stem. A method according to claim 1, characterized in that the exhaust gases are contacted with the absorbent medium in two or more steps. 98051 17. Measurement of the image of a tetroxide-containing gas in the form of a glass flask, in which case a tetrachloride, an alkyl tetrachloride or a mixture of the tin oxide is obtained frän förfarandet behandlas medelst ett förfarande enligt patentkrav 1. 20 A coating method for applying a tin oxide coating to a hot glass article, wherein the hot glass article is treated with a gas containing at least one tin compound which is tin tetrachloride, an alkyltin halide or a mixture thereof. method. A method according to claim 17, characterized in that said tin compound is recovered from the absorbent medium and recycled for use in said coating method. 18. The scope of the patent is set out in claim 17, which is based on the fact that the absorption of the medium and the circulating circuits of the present invention can be performed. 25